Radio guiding and landing system



Aug. 22, 1950 D. WEIGHTON RADIO GUIDING AND LANDING SYSTEM Filed Nov. 26, 1948 LOCAL $59- Z. Rscnvza mama RECEIVER.

/L TER FILTER FIL TE I2 FILTER B A B A DErEcTnR-(- S JZ MIXER MIXER. 9- fi f 0 cm Inventor D NA D WEIGHT-O IV Patented Aug. 22 1950 2,519,521 itiimo GUIDING AND LANDING SYSTEM D nal wgi lt miCambridg En l Q as h r A t9, ;yerL im ited, Cambridge, England; a British company A Application November 26, 1948, Serial No. 61,961

ImGfiaat Britain November :29, 1947 6 Claims. (01; 343 109) This invention relates tg radio guidin gvend nets from the transmitter in terms of the landing systems more haitidirleirlfi but notekcluseparation of the" a'erfijalS' and, theuco urse sharpsive1y, for aircraijt ness p ffthegsysten bo h i which a kn wn In a known'in'ethod 6f assisting aircraft to land 'Ihe invfi ition, w ill be. more, olearly understood in conditions bad yisibility bytradi fl i nals, fro njt ecomnan negqrawi nw i l three separate "transmittin and reeeivmggeqqip- Fig. 1'is a diagram fqr'xplaining the principle ments are required to provide respectively track q fthei elntiq y h V 1 guidance in azimiith, track guidanee in elevation, Fig. 2 showsa schematic circuit diagram .of one and an indication of distance from aselected {grin of receiving apparatus, v o t n h heirfie d; t e .jF 31s ag ph .iQr ex la nin the nve tion F gural iagramma i l shows a plan View ,Of an aircraft F approaching an airfield provided with an azimuth traek guidance transmitter T, the airerjait being provided ,with two similar ,repair g; rie n in unt d n horizontall ;spaced relation sv nmetrieaHy'td the axis of ,the "a 'cflraft; breferahly on the win tips t the air.- "raft, "'I'f'he' diiier ence in the depths ofjn' odula- 'jtionof 'thetwo 'tones received at aerial I defines "the angle 01'" bttveenffthe line T-l and the 1 '1 ne 'T -X reiires'e'ntin glthe -eemf-signal course, and the 'c liff'erenc in depth of modulation of the two 'tonesreeeived at aerial 2 defines the angle, 02 btwee'nth'e line 1-2 and'th'e lineT -X, sinc the 'relatib'nbetweenthe differenee in depthlnflhoqulation ahd'thela'njgle' of deviation fromtheboui Se liiie"is"1ii1ear for small angles, islfixed, by: the "aerial systeniof the; transmitter T, an d is generally'standardised at 2 191" the total modulation depth for onefdegree deviation ofi course. 'Thedifierence between the dififeienees in deiith or modulation d'f'the' two tQnes received at aerials 'l'and 2' is then "proportional to thearigle 0i-02 V v. H (Figure 1)', and hence is 'invers ely proportional by comparison of theiifibi'ihiiies drthtw 3 to the distance of theaire'rait F trim; the transproduced at the detector of areceiver in'the airfiter T!" A m tBIYrOV QEd in the ai ft ,a nd -craft; The men Ptheiiipths of modulation reading this difiernce' may then be calibrated 0f the "two tones 1ncreae-i1hifbinlyflfom some directly inmiles frOni'thetrafis'mitter, or briefervefry small value at'i-smalreingle "(usually abbut ably from some niiinton the course line atwhieh l'degr'eesi on"dnesideefthe'eourse li e, through 40 the aircraft'should touchdown. unity on thecourse 'lihe tij'some"very large value Errors may'be introduced if the axi'ofthe at an equal engleen theothersi de o'i the'cou'rse aircraft isnot aligned W h e t iof D- l I -proach sincetheeheet ive horizontal spacinghf According 'tojthe ihvefitiomtvvo sini'ilar-receiv- 3 e ia s; "and'EZ'iS reducedxThe errors Will "ing 'aerials" are inherited 65- th feft ii; spaced 0 however be very small for all altitudes of the airre'la'tion"symmetriealiy'towhe'l aki's' ofthe' -craft, craft likely to occur in'approach. Thus. it"inay and provision is made n thereceiver (orreceivbe .-Sh0W l th 'a r o of 3 i! in distance ers) on the'crzift for 1 asjurihg -the sum and the i5 fl n O ce i an incl n tion of the axis of8 "difierence' of the differ fees fin" the depths of degrees to the line ofapproaeh. modulationbetw'een th wb inodulatingthe j more serioujserror-may arise if there is 11 signals derived'frorri thaws eart The sum provision forr al-( mai ng the signals from theqtwo of the diff erenees in depth OflIlQdulatlQn indiaerials and theirQasspoi a-ted receivers, since "the *c'atfes'thedviatiqnojthe centre of'the'cra ft from inequality of; signal amplitude from these two "the course 'lineg and the 'rence"between the ifsourpeswill'generally be largerthan the differ- "T e i re ii it "and receiver r, r

"mm-dew ser e-ha Pi l we nd 'di t i ite iie isur lmodificetidns' end 'jadditi the aircra and O 15 with the other of the 'two'tonesere 'loea'tedon the c'ourse'li I V *abl'edto fol-10Wthisline eper'ac an".

fqifirhces if @epth p i tien indicates ence in tone ratios which it is desired to measure.

tion tively. The filters 6 and 8 select onetone do noted by frequency A, and thefilters I and 9 select the other tone denoted by frequency B. The outputs from filters I and B are combined in a mixer ID, in which a tone of the difference frequency A-B is produced. This is selected by the filter II, from the output of which a direct current is produced in the detector 12 proportional to the amplitude of this difference frequency component. In a similar manner, the outputs from filters 6 and 9 are combined in a mixer l3 to produce a tone of the difference frequency A-B which is selected by. the filter I 4,

and a direct current proportional to this. difference frequency component is derived in the detector IS. The difference betweentheoutputs from the detectors l2 and I5 is indicated in the meter I6.

In the graph shown in Figure 3, the angular positions of the receiving aerials I and 2 shown in Figure l, and represented by the angles (such as 01 and 62). between the course line T-X and the lines (such as T-l and T4) joining the transmitter T to the aerials, are plotted horizontallv as abscissae from the origin 0. The amplitudes of the signal tones A and B produced by the receivers 3 and 4 at the outputs of the appropriate filters B, I, 8 and 9, are plotted as vertical ordinates. As the receiver 3 is moved across the course l ne T-X from one side tothe other, the output from one filter 6 will increase ,from zero at a point R (ang lar deviation (in) in a linear manner as represented by the line RQA.

At the same time, the output from the other filline QS, to vero at the point S (angular devia- VVhen the receiver is on the course line T-X, the two signal outputs from thefilters 6 and I will be eq al, as shown by the intersecter 1 will decrease linearly as represented by the tion of the lines Ram and so. at the point Q on he ordinate passing thro gh the origin 0.

The receiver 4 will have sim lar characteristics. exce t that since its gain is assumed to be different f m that of rec iver 3. the slop s of the lines RPB and SP representing the out ut Volta e of its fi e s 8 and 9 res ectively will be different from those apperta ning 'to' the receiver 3. T is is s o n in Figure 3 b giving each of the lines RPB and SP a slope di ferent from that of the corr s onding lines RQA and S0. a pertaining to the rec iver 3. it"be n assumed for the purpose of illustra ion 'in Fi ure 3, that the gain of the receiver 4 is less than that of receiver 3.

When the aircr ft F is in the posit on shown in Figure l, in which the angular deviations of the aerials l and '2 from the course line T-X are 01 and 62 respectively, the amplitudes of the signal outputs from the filters 6 and I of the nates BM and DM for the abscissa 02. By similar triangles,

is- QQ-(% E mal g The'outpfit ,fi omthe filter u is prop to the product of the outputs from filters I This expression ,doesnot contain the difference QP-OQ and therefore the reading is not dependent upon smalldiiferences in gain of the two aerials and receivers. ,The actual amplitudes OP and 0Q may beheld sufficiently constant, for the requirements of the distance meter by the automatic gain oontrolof the receivers.

Whereas for the purposes of illustration and explanation of the, invention; there has been specifically described a system for track guidance in azimuth which, in accordance with the invention, is made to serve also for distance measurement, the invention is in no way limited to such a system butmay equally well be applied in a similarmanner to any similar system such as one for-providing track guidance in elevation. In that case, the two aerials in the aircraft would be mounted verticallyone above the other in spaced relation, instead of one on each wing tip as described. .The invention is also not restricted to guiding and landing systems for aircraft, but is applicable, in exactly analogous manner to that described, to any analogous marine transmitter/receiver system providing ship-to-shore track guidance.

I claim:

1. In a radio system for guiding craft by modulating a transmitter with two low frequency tones and. radiating different directional patterns for the two modulating frequencies, the combination on the craft of two similar receiving aerials mounted in spaced relation symmetrically to the axis of the craft, receiving means for detecting the signals received from said transmitter by said aerials and including means for detecting the difference .in depth of modulation of the two tones received at one of said aerials, means for detecting the difference in depth of modulation of the two tones received at the other of said aerials, and means formeasuring the difference of said differences to indicate the distance of the craft from the transmitter.

2. In a radio system for track guidance of craft by modulating a transmitter with two low frequency tones and radiatin difierent directional patterns for the two modulating frequencies, the

combination on the craft of two similar receiving aerials mounted in spaced relation symmetrically to the axis of the craft, receiving means for detecting the signals received from said transmitter by said aerials and including means for detecting the difference in depth of modulation of the two tones received at one of said aerials, means for detecting the difference in depth of modulation of the two tones received at the other of said aerials, means for measuring the sum of said differences to indicate the deviation of the craft with respect to a predetermined course line, and means for measuring the difference of said differences to indicate the distance of the craft from the transmitter.

3. In a radio system for guiding craft by modulating a transmitter with two low frequency tones and radiating different directional patterns for the two modulating frequencies, the combination on the craft of two similar receiving aerials mounted in spaced relation symmetrically to the axis of the craft, receiving means for detecting the signals received from said transmitter by said aerials and including means for balancing said signals, means for detecting the difference in depth of modulation of the two tones received at one of said aerials, means for detecting the difference in depth of modulation of the two tones received at the other of said aerials, and means for measuring the difference of said difierences to indicate the distance of the craft from the transmitter.

4. In a radio system for track guidance of craft by modulating a transmitter with two low frequency tones and radiating different directional patterns for the two modulating frequencies, the combination on the craft of two similar receiving aerials mounted in spaced relation symmetrically to the axis of the craft, receiving means for detecting the signals received from said transmitter by said aerials and including means for balancing said signals, means for detecting the difference in depth of modulation of the two tones received at one of said aerials, means for detecting the difference in depth of modulation of the two tones received at the other of said aerials, means for measuring the sum of said differences to indicate the deviation of the craft with respect to a predetermined course line, and means for measuring the difference of said differences to indicate the distance of the craft from the transmitter.

5. In a radio system for guiding craft by modulating a transmitter with two low frequency tones and radiating different directional patterns for the two modulating frequencies, the combination on the craft of two similar receiving aerials mounted in spaced relation symmetrically to the axis of the craft, a pair of receivers connected to said aerials respectively, two similar pairs of filters for receiving the outputs from said receivers respectively, one filter of each pair selecting one of said tones and the other filter of each pair selecting the other of said tones, means to combine the outputs of the filter of one pair selecting one tone and the filter of the other pair selecting the other tone and to derive from" the combined outputs a tone of the difference frequency, means similarly to combine the outputs of the remaining two filters of said pairs and to derive from the combined outputs a tone of the diiference frequency, means to derive respectively from said two difference frequency tones currents proportional respectively to the amplitudes of said difference frequency tones, and an instrument for measuring the difference between said currents.

6. In the art of guiding craft by modulating a radio transmitter with two low frequency tones, radiating different directional patterns for the two modulating frequencies, receiving the radiation at two points separated in space on the craft and comparing the amplitudes of the two received tones by measuring the sum of the differences in depths of modulation between the two tones modulating the signals received at said points to derive an indication of the deviation of the craft with reference to a predetermined course line, the improvement which consists in measuring also the difference of said differences whereby additionally to derive an indication of the distance of the craft from said transmitter.

DONALD WEIGHTON.

REFERENCES CITED UNITED STATES PATENTS Name Date Bond Nov. 25, 1941 Number 

